Implement format.arguments and format.context from standard formatting library (#5217)

* Implement `format.arguments` and `format.context` from standard formatting library

* fix compilation for clang-cuda and old gcc

* add missing exec space annotations

* final fixes (hopefully)

* fix nitpicks in `__back_insert_iterator`

Author: davebayer

libcudacxx/include/cuda/std/__format/buffer.h

@@ -0,0 +1,48 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+// SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCUDACXX___FORMAT_BUFFER_H
+#define _LIBCUDACXX___FORMAT_BUFFER_H
+
+#include <cuda/std/detail/__config>
+
+#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
+#  pragma GCC system_header
+#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
+#  pragma clang system_header
+#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
+#  pragma system_header
+#endif // no system header
+
+#include <cuda/std/__fwd/format.h>
+
+#include <cuda/std/__cccl/prologue.h>
+
+_LIBCUDACXX_BEGIN_NAMESPACE_STD
+
+// todo: implement __fmt_output_buffer
+
+template <class _CharT>
+class __fmt_output_buffer
+{
+public:
+  using value_type = _CharT;
+
+  _CCCL_API void push_back(_CharT __c)
+  {
+    _CCCL_ASSERT(false, "unimplemented __fmt_output_buffer push_back method called");
+    (void) __c;
+  }
+};
+
+_LIBCUDACXX_END_NAMESPACE_STD
+
+#include <cuda/std/__cccl/epilogue.h>
+
+#endif // _LIBCUDACXX___FORMAT_BUFFER_H

libcudacxx/include/cuda/std/__format/concepts.h

@@ -0,0 +1,69 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+// SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCUDACXX___FORMAT_CONCEPTS_H
+#define _LIBCUDACXX___FORMAT_CONCEPTS_H
+
+#include <cuda/std/detail/__config>
+
+#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
+#  pragma GCC system_header
+#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
+#  pragma clang system_header
+#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
+#  pragma system_header
+#endif // no system header
+
+#include <cuda/std/__concepts/concept_macros.h>
+#include <cuda/std/__concepts/same_as.h>
+#include <cuda/std/__concepts/semiregular.h>
+#include <cuda/std/__fwd/format.h>
+#include <cuda/std/__fwd/tuple.h>
+#include <cuda/std/__type_traits/remove_const.h>
+#include <cuda/std/__type_traits/remove_reference.h>
+#include <cuda/std/__utility/pair.h>
+
+#include <cuda/std/__cccl/prologue.h>
+
+_LIBCUDACXX_BEGIN_NAMESPACE_STD
+
+/// The character type specializations of \ref formatter.
+template <class _CharT>
+_CCCL_CONCEPT __fmt_char_type = same_as<_CharT, char>
+#if _CCCL_HAS_WCHAR_T()
+                             || same_as<_CharT, wchar_t>
+#endif // _CCCL_HAS_WCHAR_T()
+  ;
+
+// The output iterator isn't specified. A formatter should accept any
+// output_iterator. This iterator is a minimal iterator to test the concept.
+// (Note testing for (w)format_context would be a valid choice, but requires
+// selecting the proper one depending on the type of _CharT.)
+template <class _CharT>
+using __fmt_iter_for _CCCL_NODEBUG_ALIAS = _CharT*;
+
+template <class _Tp, class _Context, class _Formatter>
+_CCCL_CONCEPT __formattable_with_helper = _CCCL_REQUIRES_EXPR(
+  (_Tp, _Context, _Formatter),
+  _Formatter& __f,
+  const _Formatter& __cf,
+  _Tp&& __t,
+  _Context __fc,
+  basic_format_parse_context<typename _Context::char_type> __pc)(
+  _Same_as(typename decltype(__pc)::iterator) __f.parse(__pc),
+  _Same_as(typename _Context::iterator) __cf.format(__t, __fc));
+
+template <class _Tp, class _Context, class _Formatter = typename _Context::template formatter_type<remove_const_t<_Tp>>>
+_CCCL_CONCEPT __formattable_with = semiregular<_Formatter> && __formattable_with_helper<_Tp, _Context, _Formatter>;
+
+_LIBCUDACXX_END_NAMESPACE_STD
+
+#include <cuda/std/__cccl/epilogue.h>
+
+#endif // _LIBCUDACXX___FORMAT_CONCEPTS_H